FRESH off the finale of “Survivor 2,” CBS is putting the squeeze on its advertisers again – trying to strike while the iron is still hot.

The message this week for interested sponsors is, “If you want your ads to appear in ‘Survivor 3’ next fall, you MUST buy ads in next spring’s “Survivor 4,” knowledgeable advertising sources tell The Post.

“Whether or not they’re gonna get their way with this one is a different story,” a prominent member of New York’s advertising community said.

The move is surprising.

A shaky economy coupled with about a million other factors have turned the television industry on its head, creating what the experts call “a soft ad market.”

While every other network has been trying not to cut its asking prices for commercial time, CBS is playing hardball.

The fear, according to industry observers, is that CBS might be trying to cover its bases in case the ratings for “Survivor 4” turn out to be less than its predecessors’.

Industry experts say the original “Survivor” was unique because – unlike almost any other regular TV series – its ratings grew steadily every week.

“Survivor 2,” on the other hand, may have boasted more viewers overall, but ratings leveled off at around 28.1 million viewers each week for the bulk of its 15-episode run.

Either way, the show turned out to be one of the network’s biggest money-makers thanks to CBS’ lucrative, season-spanning deals that locked advertisers into shelling out about $325,000 for one spot each week during the show’s entire run.

Since then, CBS has allegedly jacked up the asking price for its “Survivor 3” and “Survivor 4” season-spanning ads – to a wallet-crunching $350,000 per 30-second spot, advertising industry sources said.